1. Field of the Invention
The present invention relates to an optical switching element capable of deflecting incident light in two ways, and an optical switching apparatus and an image display apparatus employing the optical switching element.
2. Description of the Related Art
Recently, a display has been playing an important role as an image device for image information. As an element for the display, and elements for optical communication, an optical storage apparatus, an optical printer, a request for developing an optical switching element achieving fast operation has been increased. Conventionally, as those kinds of the elements, an element employing liquid crystal, an element employing a micromirror, an element employing diffraction grating and so on have been used. An example of the element employing liquid crystal is shown in FIG. 1. An example of the element employing the micromirror is shown in FIGS. 2A to 5. An example of the element employing diffraction grating is shown in FIG. 6.
The optical switching element employing crystal liquid (FIG. 1) is provided with a pair of deflection boards 101a, 101b, a pair of glass substrates 102a, 102b, transparent electrodes 103a, 103b, 103c, 103d, and crystal liquid 104 sealed between the pair of the glass substrates 102a and 102b. In the optical switching element, voltage is applied to the transparent electrodes 103a, 103b, 103c, and 103d to control orientation of crystal liquid molecules and rotate a deflection face, thereby carrying out switching.
However, the liquid crystal has poor fast-response characteristics. Even one having fast response exhibits only a few milli-seconds. For this reason, liquid crystal is considerably difficult to be applied to those optical storage apparatuses, which are required fast response, such as optical communication, optical calculation, optical storage apparatus such as holographic memory, an optical printer and so on. Additionally, in the optical switching element employing the liquid crystal, the pair of the deflection boards are necessary, which decreases effective use of light. Further, the liquid crystal can not resist strong light, so that switching can not be conducted by light having high energy density such as strong laser light. Especially, in the case of using the display, higher quality image is required. However, in the current optical switching element employing the liquid crystal, disadvantages such as inaccuracy in gradation indication begin to appear.
In the optical switching element employing the micromirror, as typified by DMD (digital micromirror device) manufactured by Texas Instruments Incorporated (U.S.), many specific examples have already existed. As its structure, there are two types: one supporting the micromirror with a single hand (FIGS. 2A, 2B, and 3), and the other supporting the micromirror with two hands (FIGS. 4A, 4B and 5). As a method for driving the micromirror, there are a method using electrostatic attraction, a method using piezoelectric elements, a method using thermo actuator and so on. Although there are differences in the structure, the method for driving and so on, as its function, switching of incident light is performed by controlling the angle of the micromirror, which is rather simple.
Here, the micromirror using the electrostatic attraction will be described as an example. As the driving principle of the micromirror, the case where the micromirror is supported with the single hand (FIGS. 2A, 2B and 3) is as follows; Potential difference is given between a micromirror 105 and a driving electrode 106, which generates electrostatic attraction to incline the micromirror 105. When the given potential difference is eliminated, the previous condition gets back by spring strength of a hinge 105a supporting the micromirror 105.
In the case where the micromirror is supported with two hands (FIGS. 4A, 4B, and 5), the same potential difference is generated between the micromirror 108 and a pair of electrodes 107a, 107b oppose to the micromirror 108. Under this condition, for example, voltage applied to the electrode 107a becomes low, on the other hand, voltage applied to the electrode 107b becomes high, which occurs unbalance in electrostatic attraction generated between the electrodes 107a, 107b and the micromirror 108 respectively, thereby inclining the micromirror 108.
The light is switched based on the following conditions. In the case of the micromirror supported with the single hand (FIGS. 2A, 2B, and 3), under a condition where the micromirror 105 is not inclined with respect to incident light P100, reflection light advances in a P101 direction, on the other hand, in a condition where the micromirror 105 is inclined with respect to the incident light P100, the reflection light advances in a P102 direction. In the case of the micromirror supported with two hands (FIGS. 4A, 4B, and 5) as the same manner, under a condition where the micromirror 108 is inclined in one direction with respect to the incident light Ploo, the reflection light advances in a P103 direction, on the other hand, under a condition where the micromirror 108 is inclined in the other direction, the reflection light advances in a P104 direction.
However, response speed of the above-mentioned switching is a few micro-seconds in many cases, which is not enough to achieve fast switching. In the optical switching element employing the micromirror, an angle capable of deflecting light (angle difference between two of the reflection light is twice as large as a mechanical mirror angle of deviation). However, in the case where the optical switching element is used for the display, for obtaining high contrast, angle differences between the two reflection light P103 and P104 must be wider, thereby the response speed becomes slower.
In the optical switching element employing diffraction grating (FIGS. 6A and 6B), as disclosed in Translated National publication of Patent Application No. Hei 10-510374, with electrostatic attraction caused by potential difference between a movable mirror 109a and a lower electrode 110a, a ribbon-like movable mirror having a light reflection face moves in a quarter wavelength of the incident light P100. This produces an optical path difference in a half wavelength between a ribbon-like static mirror 109b and the movable mirror 109a, thereby generating diffraction light, and then the reflection light is switched between a zero diffraction light P105 direction and a linear diffraction light P106 direction. At this moment, with the reason that the optical path difference is controlled within a half wavelength, intensity of the linear diffraction light P106 can be controlled. In the optical switching element employing diffraction grating, only the extremely lightweight ribbon-like mirror is moved in a small distance, which can perform switching of the light, therefore, its response is fast. For this reason, the optical switching element employing diffraction grating is suitable for the fast switching.
However, for generating light diffraction, at least the two ribbon-like mirrors are necessary, and for enhancing effective use of the light, the four mirrors or more are necessary, specifically, the six ribbon-like mirrors are necessary. For this reason, in the case of using the ribbon-like mirrors arranged in linear, a whole size is difficult to be realized miniaturization. The linear diffraction light is generated with certain angles in two directions symmetrical with respect to the optical axis of the zero diffraction light. Therefore, for using the linear diffraction light, this requires a complicated optical system used for converging the above-mentioned light, advancing in two directions, into single light. Ideally, the reflection face of the static mirror 109b and the reflection face of the movable mirror 109a must be positioned on the same plane in a condition where voltage is not applied to the electrode. However, substantially, those reflection faces are not positioned on the same plane in good accuracy. For this reason, by applying small voltage to the lower electrodes 110a and 110b, fine adjustment is respectively required to perform in order that the all reflection faces are positioned on the same plane.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
The invention has been achieved in consideration of the above problems and its first object is to provide a small and lightweight optical switching element with a simple structure capable of fast response, and an optical switching apparatus employing the optical switching element.
Further, its second object is to provide an image display apparatus capable of high accuracy in gradation indication with the above-mentioned optical switching element, and of high quality image and miniaturization.
The optical switching element according to the present invention is provided with a total reflection member having a total reflection face capable of causing the total reflection of incident light, and a translucent optical extraction unit capable of switching in either a first position or a second position, wherein the first position is a position where the optical extraction unit contacts the total reflection face of the total reflection member or a position where the optical extraction unit is disposed closed to the total reflection face with an interval small enough to extract near-field light and the second position is a position where the optical extraction unit is disposed with an interval greater than the interval with which the near-field light is extracted.
The optical switching apparatus according to the present invention is arranged a plurality of the optical switching elements of the present invention in linear or two dimensional.
The image display apparatus according to the present invention displays two-dimensional image by arranging a plurality of the optical switching elements of the present invention, irradiating three-primary colors and scanning with a scanner.
In the optical switching element, the optical switching apparatus and the image display apparatus according to the present invention, when an optical extraction unit is in a second position, with a reason that a total reflection member is apart from the translucent optical unit, incident light entering the total reflection unit is caused total reflection in a total reflection face, its reflection light is guided to one direction. When the optical extraction unit is a first position, with a reason that the optical extraction unit contacts the total reflection member or is disposed close to the total reflection member, the incident light entering the total reflection member is not caused the total reflection in the total reflection face, and is guided to a direction oppose to the total reflection member via the optical extraction unit. In connection with this, xe2x80x9cthe optical extraction is disposed close to a distance with an interval small enough to extract near-field lightxe2x80x9d means a distance in which the incident light can be extracted substantially without completely contacting the optical extraction unit to the total reflection member. In addition, if the optical extraction unit is disposed close to the total reflection member up to a distance of a one-fortieth wavelength (xcex) of the incident light, equal to or more than 90% of the incident light can be extracted.